A Symmetrical Transducer Topology

[mwmkravchenko]

I met Enrique in San Diego in 1998 when he was at Pioneer. He and a bunch of Japanese engineers and technicians interviewed me one evening and I got a job offer but I stayed at TC Sounds. At that time Enrique had a sports car and trophy wife. He was like a Tom Cruise back then and he impressed me. After he left Pioneer, he teamed up with Patrick Turnmire. I met Patrick in Hong Kong in 1999. I jokingly called them Batman and Robin. They actually referred clients to me on at least two occasions. To describe Enrique in one word, it would be "charisma".

https://patents.justia.com/inventor/enrique-m-stiles

Nice memories Steve.

Mark

 

[mwmkravchenko]

A nice underhung design.

Steve where did you find this illustration?

I incorporated a voicecoil as a fit for use check. I can see this getting a little bit of experimentation in the future. If one was to incorporate inductance compensation the admirable flux density would need some massaging via the size of the magnets.

The dimensions are all mine. I was thinking of a useful motor for a woofer. Scaling of course can be accomplished for any motor size that is reasonable.

Mark

 

[mwmkravchenko]

A quick follow up. an inductance compensation sleeve. Dropped the inductance into a good midwoofer range. But as discussed we need to massage the magnets now.

Mark

 

[jackocleebrown]

@mwmkravchenko

Mark, that motor looks very handy! Some potential to cut away some steel too by the looks of the flux density plot (if you don't mind some post machining).

I'm also just admiring your spreadsheet design tool. How is the THD metric calculated, is that an approximation from the BL(x) or a full nonlinear lumped model? For the inductance calc, is that done with DC + AC (frozen permability) analysis in FEMM?

 

[mwmkravchenko]

@mwmkravchenko

Mark, that motor looks very handy! Some potential to cut away some steel too by the looks of the flux density plot (if you don't mind some post machining).

I'm also just admiring your spreadsheet design tool. How is the THD metric calculated, is that an approximation from the BL(x) or a full nonlinear lumped model? For the inductance calc, is that done with DC + AC (frozen permability) analysis in FEMM?

Yup. Agreed the motor is interesting. And there's steel to chop away for sure.

When I showed the spreadsheet to Peter Larsen he was impressed. That made me happy

The spreadsheet was an easy interface. The program is in Python. We used Libre Office as it's free. Lubre Office draw can output DXF files. So it was a beginning. We utilize all that FEMM 4.2 latest can give you. Including blocked impedance. That can take a while! The distortion is indeed the analysis possible with FEMM 4.2. The soft parts are in Calculix and Z88. The BL calculation is custom. Not always accurate. That something we saw even in our 2016 comparisons with COMSOL and ANSYS. Everyone understands these are simulations. Most of the time the B in gap is spot on. When it's not I chase down manufacturing processes. Like the time I made a prototype and charged the motor with the shorting rings in place.

BL(x) or a full nonlinear lumped model?

That was Akos's baby. Our very talented programmer. Totally a custom bit of software that he derived from a few papers that I dug up. That was my contribution to this software, all the research. My programming days stopped in 1987. He has been teasing me with a fully rewritten version in C that dumps Open Office. At times depending on the bugs in Open Office the interface can be a bit of a pain. But the past few years have been rather stable.

Our verification was a fully tested and developed, well understood driver that we did for a client using an XBL^2 motor and our simulating it i n the commercial software and our software against real world measurements. It's been a joy to use. That motor I simulated took me 35 minutes from scratch. I looked at the drawing Steve provided and did a few napkin calculations and started out.

Mark

 

[smowry]

@mwmkravchenko

I found that patent image here: https://patentimages.storage.googleapis.com/bd/e3/6b/303547fe2f4ee7/US20040131223A1.pdf, in figure 23 (Status Abandoned).

 

[mwmkravchenko]

US20040131223A1 - Electromagnetic transducer having a hybrid internal/external magnet motor geometry - Google Patents

An electromagnetic transducer, such as an audio speaker, in which magnetic flux is provided to the drive magnetic air gap(s) by both an external permanent magnet (as in conventional pole plate geometry transducers) and an internal permanent magnet (as in conventional neo or cup geometry...

patents.google.com

Abandoned is a nice thing to read.

So I will be tinkering with this one.

Thanks Steve for the reference.

Mark

 

[mwmkravchenko]

Full Skin depth and 7 point's per octave Blocked impedance.

Looking for a reasonable Pro midwoofer design.

Needs more work. But it's a start.

Mark

 

[mwmkravchenko]

I need to tease Steve a little bit!

Mark

 

[smowry]

Mark,

Here's an alternative under hung motor topology from Laurence Dickie. Turning the magnet 90 degrees was not claimed as an invention and thus this topology is in public domain.

Unlike the motor you are simulating, the above has the typical under hung characteristic of decreasing flux density in the gap from bottom to top. Whereas, your example utilizes complementary magnets to implement a uniform flux distribution in the gap. Dickie's radial topology seeems best suited for high frequency transducers.

Source: https://www.linkedin.com/pulse/radially-speaking-steve-mowry/?trackingId=VHfM0wISlL6wC4D7kwONSQ==

It would be interesting to use the above high frequency example's geometry in a coaxial 2-way implementation.

 

[mwmkravchenko]

There are much simpler underhung motor designs. A radial magnet is definitely possible. It adds expense to the assembly. And limits the potential magnet vendors. There are only a few in China that can both make and charge a radial magnet. Then you have complex shipping requirements as well as you have complex assembly requirements.

What you posted is a good, viable design. It is simply costly. The other posted motor you started out with as an underhung has the attraction of being able to be charged in a conventional magnetizer. Greatly reducing the cost per driver.

Or you can go with a regular axially charged ring magnet and do this:

I've designed and produced different sizes of these for a few different OEM's

This particular one gets you a linear B field for an 8mm one way excursion.

Mark

 

[smowry]

@mwmkravchenko,​

That midrange looks great! Do you have more information on the surround? Why did you choose that topology?

 

[mwmkravchenko]

@mwmkravchenko,​

That midrange looks great! Do you have more information on the surround? Why did you choose that topology?

Thanks Steve. The surround and cone is the labour of quite a few weeks of tinkering and getting it right. It's not open tooling. When my client want a truly neutral driver this is the combination that I go to. Many ask for paper composite cones. I tell them this is the most neutral. I end up making them both. And they always pick the aluminium cone.

This is optimized as a midwoofer. Has enough excursion to act as one too.

 

[smowry]

@mwmkravchenko​

Can you post the frequency response? How about a front view picture? I would love to try out my new FINEsuspension/cone so that the displaced shape can be observed. I am especially interested in Sd(x). I had previously proposed 3 to 5 surround convolutions.

 

[mwmkravchenko]

So this is 90db at a one metre equivalent, that is 2 metres groundplane measurement. Almost all the extant distortion measurements are taken in the nearfield and extrapolated to 1 metre. In other words they are not exactly real. They look good, but they are not real 1 metre measurements. The difference being the excursion needed to get the SPL greatly favours a nearfield impressively low distortion measurement. This is the real deal. It is at 2 metres.

BL plot was verified via direct measurement via four points on the clock and over the gap height. It took me a few days to linearize the gap like this. It is not exactly easy.

As for cone and surround profile, these are proprietary drivers. The tooling is not open. I have posted a few pics online before, so I will repeat them here. A profile pic will not be posted.

 

[smowry]

I have been searching for a way to reduce Sd(x) nonlinearity in woofers. Purifi has their new surround and it's effective. Their surround is both positive roll and negative roll depending on position. I see a major challenge to implementing the transition from positive to negative (up and down). However, I recall a case where the transition is almost convenient. That case being a "Racetrack" surround topology. I worked on a Racetrack Surround that Genelec claims to be an invention. We disagreed, so I requested that I not be listed as an inventor; although, I was the team leader for that project. Dr. Roger Mark, the transducer group, TRES scientist at Bose had done research on Racetrack Surrounds. His surrounds had huge rolls on the turns but typical size or smaller rolls on the straight sections. The Racetrack surround can be divided into four (4) segments that are essentially independent to each other. Having said that, two (2) segments can be made positive and two (2) segments can be made negative.

https://patentimages.storage.googleapis.com/e8/b9/8e/461004bbb252ea/DK3008917T3.pdf

They left my name on the EU Patents and published my address without permission! That address is my correct home address, WTF?

Mark can you simulate 3D geometry?

 

[mwmkravchenko]

Mark can you simulate 3D geometry?

I can simulate a segment, or 360 degrees worth of segments. As far as the software is concerned a single pie piece is all that is required, unless you have a non linear surround like you have here. I never set this up in the present software.

What I have learned from the underhung work I have been doing over that past 8 years is that if you have a linear conventional surround and a very linear motor you have as good distortion numbers as you have with the Purifi. The difference in testing is what makes the Purifi numbers appear better. Knowing the entire train of testing conditions, modeling and design is not discussed enough. Conventional overhung motors can be a source of distortion if the designer is not attentive to their weaknesses. That statement is true of any motor. But it is aimed at the predominant motor topology.

Furthermore, trying to model a surround for more than mechanical movement purposes is in my opinion trying to catch the wind. I have never had a surround vendor give me the material properties of what they use in the molding. And having visited a few of them I know that they keep that proprietary. So our modeling is using what parameters? You could characterize a piece of a known surround. This is true. Again, you are hoping that you will get the same exact materials in your batch of surrounds. What We try to do is use rapid iteration methods. Resin print the dies, get them made and physically tested. Part of the reasons why I travel to China for deeper R&D is that it is both rapid and inexpensive compared to Canada. Having done the home work first makes it all happen more rapidly. Having good relations with your cone factory is truly important. We can accurately simulate the motors. The moving parts, not so much. We get reasonably useful. Not as accurate as the magnetics.

Sucks about your address. When are you there for a visit

 

[smowry]

@mwmkravchenko wrote, "Sucks about your address."

The whole situation sucked. Stephen Millar copied the Paradigm Electronics Inc. Patent and applied it to the round segments of the Genelec Racetrack Surround and I do mean copied. I sent him that Patent Reference and like two (2) days later he claimed an invention. Stephen Millar was Genelec's COMSOL mechanic.

https://patentimages.storage.googleapis.com/0c/10/06/33682fb8b9073a/US8340340.pdf

So essentially, we took Dr. Mark's Racetrack Surround and substituted the Paradigm geometry for the two (2) round segments of the Racetrack Surround. Genelec then claimed an invention; I disagreed based on guess what, engineering ethics. So I asked that my name be removed from the Patent documentation. Then Genelec did not even site the Paradigm Patent within their application or grant.

Application: https://patentimages.storage.googleapis.com/8f/6b/5d/7608a3420308d9/US20160142825A1.pdf (contains my name)
Grant: https://patentimages.storage.googleapis.com/0a/91/5d/345c85f7ac4139/US9838793.pdf (my name removed per my request)

I wanted Roger credited and US8340340 cited within their Patent documentation! US9838793 was the first surround Stephen Miller ever designed. Was it invention or innovation?

And that's the Phuket Report.

 

[mwmkravchenko]

Frankly, most folks are proud to have Patent credits, whereas I am proud that I have no patent credits but I do claim to have ethics! Transducer Engineering is an honorable profession and patents should not be treated similar to dirty rags but unfortunately many times they are. My preference was to publish and share ideas in hopes of moving the industry forward.

I prefer to have someone buy a product and try to actually reverse engineer it. At least it's sporting.

As for innovations in transducer design. Tiny. This is a very mature field of engineering. What we can do is apply something in a better way, or with better materials. I always ask myself how on earth patents like the one you cited get past the examination stage. If people with no patent examiner qualifications can cite reasons they should be excluded what is the point of a patent examiner in the first place? Asleep? Incompetent?

If there is innovation having ones name on it is a badge of honour.

 

[Timcognito]

Patents help protect exploitation of someones life work. Those with resources learn from your work innovate and lock you out of your own expertise your by enhancing prior art patenting it. If one receive a patent nothing stops one from licensing it a modest fee or royalty. Such is the way of universities to receive operational funds and collaborations with outside organizations which in turn hire more people. It is not black and white and what one does with one's ideas is okay and their choice.